The invention relates to an apparatus for monitoring a high voltage vehicle power supply system of an electrically operable vehicle for the presence of an overload. The high voltage vehicle power supply system comprises, as components, one or more energy sources and/or one or more energy sinks that are connected via a respective conductor run arrangement to a first supply potential line and a second supply potential line.
To protect individual conductor runs in a high voltage vehicle power supply system, fusible links matched to the respective different current intensities and line cross sections are used. The fusible links are designed to trip in the event of a very large flow of current as a result of low-resistance connection of the live conductors, in order to protect the component or components connected to the relevant conductor run from destruction or damage. On account of the limited space available in a vehicle, the fusible links are not arranged in a separate fuse distributor, as is known from fuses in a low voltage vehicle power supply system (12 V vehicle power supply system). Instead, existing components, such as e.g. a charging device or power electronics, have additional current connections fitted that are provided with fuses in these components.
Fusible links have a relatively high degree of variance in terms of the current from which they trip. In addition, the current, referred to as the tripping current, is dependent on the ambient temperature. If the tripping current at the fusible link is now larger than a continuous current design of the conductor run to be protected, then an overload situation can arise that results in damage to the conductor run and possibly to the components connected thereto. In order to be able to safely rule out an overload situation, the lines of a respective conductor run need to be provided with a high level of overdimensioning, such that the tripping current of the fusible link is ideally smaller than the permitted continuous current through the conductor run. This results in increased weight for the vehicle, however, which in turn adversely affects energy efficiency.
It is the object of the present invention to provide an apparatus for monitoring a high voltage vehicle power supply system of an electrically operated vehicle for the presence of an overload in which no overdimensioning of the lines of a conductor run arrangement of the high voltage vehicle power supply system is necessary.
This and other objects are achieved by an apparatus for monitoring a high voltage vehicle power supply system of an electrically operable vehicle for the presence of an overload, wherein the high voltage vehicle power supply system comprises, as components, one or more energy sources and/or one or more energy sinks that are connected via a respective conductor run arrangement to a first supply potential line and to a supply potential line. It goes without saying that a component is also intended to be understood to mean a component that is both an energy source and an energy sink.
Each of the components have an associated current sensor that is designed to register a current flowing through the relevant component and to transmit a piece of information representing the level of the current to an evaluation unit for evaluation, wherein the evaluation unit is designed to compare the current with a first current threshold and a second current threshold and to output a disconnection signal at least for the component associated with the current sensor when, as a first criterion, the level of the current and the period of the level of the current is between the first and second current thresholds.
A respective current sensor may, by way of example, be realized in the form of a shunt or a Hall sensor. In principle, however, any desired sensor can be used that permits the current flowing through one or more components of a conductor run to be measured.
The evaluation unit may be for example a separate controller or a particular microcontroller in a controller that is already in place in the vehicle. The evaluation unit may alternatively also be realized in software and run on a controller that is already in place in the vehicle. Such a controller could, by way of example, be a disconnection device that ensures that the high voltage vehicle power supply system performs isolation of energy sources from the remainder of the high voltage vehicle power supply system in the event of an accident. In this regard, an appropriate disconnection device is typically connected to the relevant components to be disconnected via dedicated hardware lines.
The disconnection signal can, by way of example, be used by a device for processing the disconnection signal, in such a way as to disconnect at least the components associated with the current sensor or just to restrict the power of said components. The disconnection signal can also be used to isolate all energy sources from the high voltage vehicle power supply system.
The apparatus allows an overload to be detected that is situated as a result of a current between the permitted current in the normal situation (first current threshold) and the tripping current of a fuse element, such as e.g. a high voltage fusible link. The apparatus allows large line cross sections of the conductor run arrangement and resultant demands on corresponding plug systems to be dispensed with. Furthermore, high integrity demands are met by the apparatus. The overload protection can be designed very precisely by virtue of the choice of appropriate values for the first and second current thresholds. The apparatus is inexpensive to provide, since only additional costs for providing the current sensors are incurred.
The apparatus can be realized alternatively by hardware circuits and/or software, allowing high integrity levels (automotive security integrity level, ASIL). The apparatus furthermore allows the disconnection of a component to be reset in an overload situation by virtue of appropriate actuation of the evaluation unit. This makes resetting simpler and quicker to perform in comparison with replacement of a fusible link. Short-circuit protection by fuse elements can be designed exclusively for the short-circuit situation and does not need to take account of the overload situation. This allows erroneous tripping instances to be avoided for high operating currents, whereas isolation capability is ensured for high currents.
According to one configuration, the first current threshold is represented in a current/time graph by a prescribed first characteristic curve that has a first section in which the current has a first, high current value from a first time to a second time and that has a second section in which the current has a second, comparatively lower current value from the second time. The first characteristic curve therefore corresponds for example to the permitted current in the conductor run arrangement in the normal situation. In this case, the permitted current in the normal situation allows an increased switching-on current to be drawn for a particular time. By contrast, a decreased continuous current is provided in the normal situation.
The first current threshold can also be chosen arbitrarily, in order e.g. to tolerate a certain degree of overload beyond the normal situation. The first characteristic curve is then situated to the right of the permitted current in the conductor run arrangement in the normal situation.
According to a further configuration, the second current threshold is represented in a current/time graph by a temperature-dependent, nonlinear family of characteristic curves that has a substantially exponentially falling profile. The greater the temperature (e.g. the ambient temperature), the smaller the difference between a current value of the first current threshold and a current value of the second current threshold at one and the same time. The profile of the family of characteristic curves in the current/time graph and particularly the distance between a current value of the first current threshold and a current value of the second current threshold at a particular time can be chosen by virtue of design and dimensioning of a fusible link. In principle, it is expedient if each current value of the second current threshold at any time is larger than the current value of the first current threshold at the same time, in order to have no undesirable tripping of the fuse in an uncritical operating situation.
According to a further configuration, the evaluation unit is designed to additionally compare the current with a third current threshold and to output a disconnection signal at least for the component associated with the current sensor when, as a second criterion, the level of the current is between the second and third current thresholds. In this case, the third current threshold corresponds to the line characteristic curve stipulated by the thickness and the cross section of a line.
The third current threshold is represented in a current/time graph by a temperature-dependent, nonlinear characteristic curve that grasps a substantially exponentially falling profile and corresponds to the line characteristic curve. The lower the ambient temperature of the vehicle, the greater the difference between a current value of the third current threshold and a current value of the second current threshold at one and the same time.
The high voltage vehicle power supply system can include a disconnection device that isolates current sources from the first and second supply potential lines using a tripping signal, wherein the disconnection device is designed to generate the tripping signal in the event of an acceleration, ascertained by a sensor, that exceeds a prescribed limit value, the disconnection signal output by the evaluation unit being suppliable to the energy sources as a tripping signal. This allows the component or components connected to a conductor run to be isolated from the high voltage vehicle power supply system in an overload situation, by means of components that are in place in a vehicle.
The evaluation unit may be designed to output the disconnection signal only when the third criterion satisfied is a prescribed period since the time of the onset of the first, and optionally also the second, criterion. In this case, the length of the prescribed period may be dependent on the level of the measured current. According to this configuration, it becomes possible to distinguish the overload situation between an uncritical region and an unprotected region. The uncritical overload situation exists when the current registered by the current sensor is between the permitted current through a conductor run in the normal situation (first current threshold) and the current characteristic curve of the continuous current design (third current threshold value). A direct risk to the line and the component connected to the line does not exist. By contrast, immediate disconnection is effected if there is a critical overload situation in which the measured current is between the current characteristic curve of the continuous current design of the line (third current threshold) and the tripping characteristic curve of the high voltage fusible link.
In order to inform the driver or a workshop that an (uncritical) overload situation has arisen, the evaluation unit may be designed to output a diagnosis or fault signal when the first and/or the second criterion is satisfied.
The evaluation unit may further be designed to store one or more of the following pieces of information in a memory on the onset of the first and/or second criterion: an identifier of the current sensor that has registered the increased current exceeding the first current threshold; the level of the measured current; the period of occurrence of the increased current. As a result, by reading the relevant piece of information or pieces of information, it is possible to establish, for example during a workshop visit, that, and even in which conductor run, a fault is occurring. This facilitates fault finding and correction.
According to a further configuration, the conductor run arrangement has one or more fusible links provided in it, wherein each fusible link, when a prescribed current that is larger than the second threshold value is exceeded in the conductor run section in which the relevant fusible link is arranged, trips to protect the components connected to the conductor run.
Each component can have an associated fusible link. Alternatively, multiple components can have an associated shared fusible link.
In a further configuration, each component can have an associated current sensor. Alternatively, multiple components can also have an associated shared current sensor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.